The present invention relates to a liquid crystal display apparatus of an active matrix system wherein a number of TFT (thin film transistors) are arranged together with pixel electrodes, and a manufacturing method thereof.
With respect to patterning methods for a TFT array substrate for a liquid crystal display apparatus using TFTs, two methods are mainly used:
one is a batch exposing method in which, by using a conventional large-size mask, an exposing process is applied at one time to a display area constituting the liquid crystal display apparatus and a panel peripheral portion including a wiring portion for transmitting scanning signals and data signals to the display area from external circuits or a transfer pad for applying a voltage to a counter substrate; and
the other is a divisional exposing method in which the display area and the panel peripheral portion, which are divided into a plurality of small masks, are exposed while they are repeatedly shifted on the array substrate.
The main feature of the batch exposing method is that no border line appears on the pattern on the array substrate since an electron beam or a laser beam is used so as to directly draw patterns in the pattern drawing method upon manufacturing the large-size mask; however, the disadvantages of this method are that the mask is very expensive and that the pattern is not changed easily. In contrast, the division exposing method, which uses inexpensive masks as compared with the batch exposing method and allows easy alternation of the pattern, have been widely used; however, the disadvantage of this method is that a plurality of border lines appear on the display area due to the divided masks.
As described above, in the division exposing method, since a plurality of border lines appear on the display area, fine differences in the finishing precision of patterns on both of the sides of the border lines give adverse effects on the display characteristic, with the result that the differences in luminance on the borders become conspicuous, and are visually recognized as so-called shot unevenness. Moreover, recently, as the liquid crystal display apparatuses have been improved to have high quality and high precision, variations in the aperture ratio, the occurrence of domains and dispersions in the gradation setting at the time of assembling the panel into the module due to fine process dispersions, which have conventionally not raised any problems, now raise the problem of emphasizing the shot unevenness. Here, it is well known that, although the visibility of the human eye is very high in recognizing regular pattern layouts and differences in luminance, it is relatively low in the recognition of patterns that gradually change over a wide range. Therefore, the object of the present invention is to improve the quality of the liquid crystal display apparatus by making the display unevenness less conspicuous by utilizing the vagueness of the visibility of the human eye, and to widen the margin of the process by absorbing process dispersions, without causing a reduction in the yield of processing products.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 1 of the present invention, which is used in a liquid crystal display apparatus including:
(1) a TFT array substrate having a plurality of scanning lines formed on a transparent insulating substrate by a metal film, a plurality of data lines formed on or beneath the scanning lines so as to be separated by an insulating film in such a manner as to intersect the scanning lines, switching elements that are formed by a semiconductor layer at respective intersections between the scanning lines and the data lines, and pixel electrodes that are formed by a transparent conductive film and electrically connected to the switching elements; and
(2) a counter substrate provided with a liquid crystal interposed between the TFT array substrate and the counter substrate;
wherein a divisional exposing method is adopted as a patterning method on the TFT array substrate, so that adjacent exposing areas within a display area of the liquid crystal display apparatus have overlapped portions with each other being divided into a plurality shots, and so that a shot layout is defined in such a manner that, within the overlapped exposing areas; wherein the portion which comes closer to a predetermined shot area is subjected to a greater distribution of the predetermined shot.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 2 of the present invention, which is used in a liquid crystal display apparatus including:
(1) a TFT array substrate having a plurality of scanning lines formed on a transparent insulating substrate by a metal film, a plurality of data lines formed on or beneath the scanning lines so as to be separated by an insulating film in such a manner as to intersect the scanning lines, switching elements that are formed by a semiconductor layer at respective intersections between the scanning lines and the data lines, and pixel electrodes that are formed by a transparent conductive film and electrically connected to the switching elements; and
(2) a counter substrate provided with a liquid crystal interposed between the TFT array substrate and the counter substrate;
wherein a divisional exposing method is adopted as a patterning method on the TFT array substrate, so that adjacent exposing areas within a display area of the liquid crystal display apparatus have overlapped portions with each other being divided into a plurality shots,
wherein a shot layout is defined in such manner that, within the exposing areas having quadruple overlaps; wherein the portion which comes closer to a predetermined shot area is subjected to a greater distribution of the predetermined shot.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 3 of the present invention is arranged so that, within the overlapped exposing areas, the shot is selected by using a pixel size as one unit.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 4 of the present invention is arranged so that, within the overlapped exposing areas, the shot is selected by using random numbers.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 5 of the present invention is arranged so that, within the overlapped exposing areas, the ratio occupied by a predetermined shot is selected in proportion to the distance from the border between one of the predetermined area and the other area of a different shot.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 6 of the present invention is arranged so that the overlapped exposing areas have a width greater than 4 mm.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 7 of the present invention is arranged so that, within the overlapped exposing areas, a shot adjacent to a different shot is allowed to have a multi-exposure area of 1 to 5 xcexcm.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 8 of the present invention is applied as a patterning method to any one of steps of forming the scanning-line, forming the semiconductor-layer, forming the data-line and forming the pixel-electrode.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 9 of the present invention is applied to a plurality of steps among the steps of forming scanning-line, forming the semiconductor-layer, forming the data-line and forming the pixel-electrode, wherein the same shot layout is used within the overlapped areas among the above-mentioned applied steps.
The manufacturing method of a liquid crystal display apparatus in accordance with claim 10 of the present invention is applied to a plurality of steps among the steps of forming scanning-line, forming the semiconductor-layer, forming the data-line and forming the pixel-electrode, wherein individually independent shot layouts are used within the overlapped exposing areas among the above-mentioned applied steps.
The liquid crystal display apparatus in accordance with claim 11 of the present invention is manufactured by using the method of claim 1.
In other words, the present invention, which uses the division exposing method, allows the visibility to luminance differences to become vague by preventing apparent border lines from being formed within the display area. More specifically, a plurality of adjacent shots are allowed to have overlapped areas, each having not less than a predetermined width, with each other, and the overlapped areas are exposed by any one of shots, with the shots other than the selected shot being light-shielded by light-shielding patterns on the mask, thereby making it possible to prevent duplicate shots. Moreover, in order to allow the human visibility to the border portion to become further vague, it is effective to carry out the selection of shots within the overlapped areas by using random numbers.
An idea similar to the present invention has been proposed by Dainippon Insatsu K.K. as a method for manufacturing a large-size mask (see Japanese Unexamined Patent Publication No. 143513/1990, Japanese Unexamined Patent Publication No. 143514/31990 and Japanese Unexamined Patent Publication No. 144535/1990.) This method was used as a patterning method for exposing a large-size mask substrate by combining a plurality of small-size masks in those days when a conventional direct drawing method using an electron beam, a laser beam, etc. could not be applied to the large area of a large-size mask. Here, in the case when this method is used in a large-mask manufacturing pattern, although it is possible to make less conspicuous the border lines due to differences in finished shapes on the large mask, the positional relationship between patterns on the large-size mask is always the same. Therefore, an array pattern, manufactured by a large-size mask using this method, always contains errors in the processed state at the time of the large-size mask formation, and even if these errors are not preferable for the electrical characteristics, the relationship cannot be changed. In contrast, in the case when this method is applied to the division exposing system, since a correction can be made for each shot, it is possible to improve the electrical characteristics by adjusting the fine positional relationship between adjacent shots. The present invention develops this idea as a manufacturing method for TFT array substrates, and solves problems encountered in actually applying the idea to the manufacturing method for TFT array substrates.
One of the features of the present invention is that a process to which the present invention is applied can be freely selected. In other words, in a liquid crystal display apparatus in which the present invention is used, a process which is likely to cause shot unevenness due to its array structure and driving system may be predicted, and the present invention is applied only to such a process, while the other processes are carried out in such a manner as to leave apparent border lines as in the conventional method. In contrast, by applying the present invention to a plurality of processes so as to provide a plurality of parameters to the shot unevenness, it is possible to make the luminance differences less conspicuous. Moreover, in the case of adjacent different shots, a duplicate exposing area is formed along the border so that it is possible to prevent formation of unwanted patterns and loss of necessary patterns due to dispersions in the positional precision in the exposing device and the mask. The following description will discuss functions of the present invention. For convenience of explanation, an explanation will be given of a case in which the present invention is applied only to one process. FIG. 1 is a schematic plan view showing a shot border portion in the case when a conventional division exposing system is used.
In FIG. 1, reference numeral 1 shows one of adjacent shots 1; reference numeral 2 is another of adjacent shots; and reference numeral 3 shows a border line between adjacent shot 1 and shot 2. Since 1 and 2 have no overlapping areas, an apparent border as shown by reference numeral 3 is formed; thus, parameters with respect to the display characteristics tend to vary between the right side and the left side of the border 3 due to dispersions in the mask precision and the process finishing.
FIG. 2(a) is a schematic plan view showing the present invention. In FIG. 2(a), reference numeral 1 shows one of adjacent shots 1, reference numeral 2 shows another of the adjacent shots 2, reference numeral 31 shows an overlapped area between the shot 1 and shot 2. As indicated by reference numeral 31, each of shot 1 and shot 2 has an overlapped area of not less than a predetermined width, and has no apparent border. Reference numeral 32 shows an area in which a process other than the applied process (hereinafter, referred to as the other process) belongs to shot 1, and reference numeral 33 shows an area in which the other process belongs to shot 2. Moreover, in order to explain functions of the present invention more clearly, the overlapped area 31 is shown in FIG. 2(b) in an enlarged manner. In FIG. 2(b), reference numeral 41 shows an area in which the other process belongs to shot 1 and the applied process belongs to shot 1, and reference numeral 42 shows the other process belongs to shot 1 and the applied process belongs to shot 2. In the same manner, reference numeral 43 shows an area in which the other process belongs to shot 2 and the applied process belongs to shot 1, and reference numeral 44 shows an area in which the other process belongs to shot 2 and the applied process belongs to shot 2. As described above, even when the applied process of the present invention is limited to one process, four combinations of shots between the applied process and the other process exist within the overlapped area, and as shown in FIG. 2(b), four parameters, which give effects on the display characteristics, are randomly placed without having apparent borders, thereby making the luminance differences less conspicuous.